tree: Remove unused <string.h>

Change-Id: I9ed1a82fcd3fc29124ddc406592bd45dc84d4628
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82666
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Yidi Lin <yidilin@google.com>

src/include/bootstate.h

@@ -3,7 +3,6 @@
 #define BOOTSTATE_H
 
 #include <assert.h>
-#include <string.h>
 #include <stddef.h>
 /* Only declare main() when in ramstage. */
 #if ENV_RAMSTAGE

src/include/rmodule.h

@@ -4,7 +4,6 @@
 
 #include <stdint.h>
 #include <stddef.h>
-#include <string.h>
 #include <commonlib/rmodule-defs.h>
 
 enum {